Farm Progress

Soybean Source: Follow the label carefully when using new dicamba herbicide products.

March 23, 2017

6 Min Read
NEW TOOLS: Directions for use and restrictions on labels are considerable for the new dicamba herbicides for dicamba-tolerant soybeans. Check up-to-date labels or websites for information. The real risk is the liability that goes along with not following the label.

By Clarke McGrath

After a decade or more of research, testing and a long regulatory process, it is “game time” for the Xtend dicamba-tolerant (DT) soybean system. While we have experience with dicamba herbicide in corn, there are a lot of differences in how we have to handle it in soybeans. There is a lot of discussion about the DT system as we head into spring, especially with the herbicide labels changing so frequently — sometimes on a daily basis. So with the help of the Iowa State University Extension crops team, I put together a set of questions and answers — as we understand them right now.

Since the labels are evolving so quickly, work with your local retailer and check the DT system herbicide (Engenia, XtendiMax and FeXapan) websites to get the most current information. We always have to say this — “the label is the law” — and one of the first things these new labels point out is that you have to have the latest (within the last seven days) supplemental label in your possession at the time of application. As complex as these labels are, my bet is you’ll be glad you have one with you. Since we can’t cover all the specifics of the labels here, we’ll focus on issues generating a lot of discussion.

Can I use one of the new dicamba products — Engenia, FeXapan or XtendiMax — as a burndown ahead of my Xtend beans? You bet, and to me this is one of the best fits for the system given the challenges we have with some of our no-till/minimum-till weeds. Here are a couple of other questions that have come up about these early applications:

Do we need to watch the temperature? Experience with cool-weather applications of dicamba (and most other herbicides) has taught me that the best strategy to maximize efficacy — especially with hard-to-control weeds, or weeds pushing label height restrictions — is to hold off on spraying until it warms up, if feasible. There aren’t any specific label recommendations yet, so experts often recommend avoiding burndown applications when nighttime temperatures are below 40 degrees F, and that allowing for several days of warmer weather prior to application may result in more effective control than applying on the first warm day. By "warm," many resources mention daytime temps in the high 50s or above, and nighttime temps above 40 degrees. There is a great discussion of the topic here.

Can we use generic dicamba in our burndown? Not really. Technically for a burndown, it would be possible, but the very long and restrictive planting intervals mean from a practical perspective, the answer is no.

Can we use generic dicambas over the top? This is a definite no. Only the three new products are labeled for applications to DT beans. A primary reason is that the new products use various tactics to reduce volatility, one of the biggest risk factors with dicamba. Experts are also quick to point out that in the terms of liability insurance coverage, if a non-labeled dicamba is used and there are any claims, it voids the policy and the applicator is liable. The bottom line is that since we appear to have ample supplies of the three relatively cost-competitive new formulations, there’s no reason to apply other formulations off-label.

Is the new dicamba system the answer to our waterhemp/Palmer amaranth challenges? No, it’s not the answer, but it can be a decent tool in the fight. You'll still have to use other strategies like multiple effective sites of action, full rate residuals and the rest of the tools we have in fighting problem weeds. The labels for the DT system herbicides illustrate this pretty well; for example, they say to spray when weeds are less than 4 inches tall. If you have experience with dicamba, then you probably concur with that guideline.

We’ll want to follow the Xtend system requirements to the letter to make it successful. If we don’t, we could bury the Xtend system in short order. In 2015, a researcher from Arkansas transferred Palmer amaranth from a soybean field to a greenhouse and sprayed the first two generations with dicamba at sublethal doses. After growing out seed from survivors, the third generation was resistant to a full label rate of dicamba. The takeaway is that without trait stewardship, dicamba resistance could potentially happen in a field in three years.

How do the new DT beans yield? Great question, especially with some states north of us sharing some data that had DT beans a bushel or 2 behind other systems (Roundup Reay 2 Yield, for example). Seeing this prompted me to take a long look at Iowa yield data sets from a multitude of sources over the last couple of years. Based on that, in my opinion, if we match agronomic traits with the right fields, DT soybeans will be right there with the other genetics.

It looks like our Iowa maturity group range has the longest list of DT varieties to pick from — potentially allowing for more accurate variety placement — so this could explain why northern states with fewer varieties to choose from saw the results they did. After looking at so much yield data, I’d say the same thing about most of the other soybean systems. Every lineup has a few racehorses and dogs, but overall we have access to a lot of great genetics.

What about the wind speed restrictions and my neighbor’s non-Xtend beans, grapes and gardens? This is where reading the label for the exact product you are using is really important. There are some significant differences between them. We can’t touch on all of the differences here, but one section specifically prohibits spraying when the wind is blowing — at any speed — in the direction of specialty crops. For XtendiMax and FeXapan, this includes non-DT soybeans. A buffer isn’t an option; you simply can’t spray if there is any wind in that direction.

The Engenia label lists non-DT beans under "sensitive areas," instead of specialty crops, meaning you can spray Engenia in fields where the wind is blowing up to 10 miles per hour (but no inversion) toward a non-DT soybean field if you have a 110-foot-wide buffer.

Speaking of wind inversions, we could dedicate an entire article to that topic. Luckily, they are explained pretty well in the herbicide labels since they can (and did in 2016) create havoc with dicamba. And you could have guessed it; application rules related to inversions are another area where the labels differ among products.

On the topic of specialty crops, consider visiting and signing up for the DriftWatch program. It can help with identifying locations of sensitive and specialty crops like vineyards, nurseries and vegetable production near your fields.

After the fallout from illegal dicamba applications to soybeans in 2016, we’ll want to be on our best behavior with any dicamba herbicide applications. As both an applicator and a trainer working with Iowa’s private and commercial applicators, I know we can handle the responsibilities that come with the use of dicamba on DT soybeans. Be safe, good luck this spring, and “read and follow label directions.” You knew I had to say that one more time!

McGrath is the On-Farm Research and Extension coordinator for the Iowa Soybean Research Center at Iowa State University.

See Related: Use dicamba legally and successfully

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